Method for producing crude oil

ABSTRACT

The invention describes a method for injecting a fluid into a crude oil-containing layer of rock or earth by means of a suitable line, wherein the line is introduced into the layer of rock or earth and the fluid is injected for the purpose of an enhanced crude oil production from the crude oil-containing layer of rock or earth.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from German Patent Application No. DE 102008052465.4, filed Oct. 21, 2008, and German Patent Application No. DE 102009038445.6, filed Aug. 21, 2009.

BACKGROUND OF THE INVENTION

The invention relates to a method for injecting a fluid into a crude oil-containing layer of rock or earth by means of a suitable line, wherein the line is introduced into the layer of rock or earth and the fluid is injected for the purpose of an enhanced crude oil production from the crude oil-containing layer of rock or earth.

Crude oil is typically located in crude oil reservoirs close to and below the earth's surface. Depending on the depth of the reservoir, the crude oil is recovered from these reservoirs in open cast drilling, as in the case of the Canadian oil sand fields, but mostly in drift drilling or by means of drilling platforms, which provide for a production in the middle of the ocean. Crude oil is mainly recovered in drift drilling. For this purpose, conveyor lines are introduced underneath the earth's surface as far as the depth of the crude oil reservoir by means of boreholes. The crude oil is recovered from the crude oil reservoir via this conveyor line.

The production thereby substantially takes place in three phases. In a greater depth, the crude oil is under the pressure of the superimposed load of the layers of earth and of the associated crude oil carrier gas, if applicable. In the first phase, the crude oil can often be produced without additional measures by means of the inherent pressure in the reservoir. In response to the decrease of the inherent pressure, the oil can be conveyed to the surface by means of technical resources, such as subsurface pumps.

As a rule, the inherent pressure of the crude oil reservoir alone is no longer sufficient for transporting the crude oil to the earth's surface after a production of from 10% to 15% of the quantity available in the reservoir. This phase of the primary crude oil production is thus followed by the phase of the secondary production. In this second phase, the reservoir pressure is increased by pumping water, steam or gas via lines, which have been introduced into the earth by means of boreholes. According to the state of the art, water is typically re-pumped in this phase, whereby it is possible to convey between 30% and 40% of the oil, which is originally present in the reservoir (original oil in place or OOIP) to the earth's surface. The residual oil, which remains in the reservoir and which is increasingly ductile and dense, complicates a further constant production. Additional oil can be conveyed out of the reservoir only via special methods for the tertiary crude oil production.

According to the state of the art, different fluids are pressed under pressure into the vicinity or directly into the reservoir, respectively, by means of suitable lines in this phase of the crude oil production. Among others, heat methods such as the pressing in of hot water or superheated steam or the pressing in of gases such as nitrogen and carbon dioxide are known hereby. On the one hand, carbon dioxide increases the pressure in the reservoir, but on the other hand also dissolves in the crude oil under suitable conditions. The viscosity of the crude oil is considerably reduced by means of the carbon dioxide dissolved in the crude oil and the production is thus improved.

Such a method for the tertiary crude oil production is described in patent publication GB 2 379 685. In the state of the art described in GB 2 379 685, a second line is introduced into the crude oil reservoir parallel to the conveyor line of the crude oil for supplying a fluid. A fluid consisting of water, steam, steam foam or foam, nitrogen and/or carbon dioxide is pressed into the crude oil reservoir via this second line. Preferably, water or an aqueous solution or foam, respectively, is hereby used. According to the state of the art disclosed in GB 2 379 685, the line for injecting the fluid consists of two different sections. Both sections are separated by means of stoppers, which are typically called “packer” in the oil industry and which can be separately exposed to the fluid. The fluid is pressed into the different areas of the crude oil reservoir via the two different sections in such a manner that the supplied quantity of the fluid varies cyclically and asynchronously. The method is described as being particularly suitable for crude oil reservoirs, which appear in geological formations, which encompass cracks or gaps. By means of the method described in GB 2 379 685, the proportion of water in the water-crude oil mixture conveyed via the conveyor line is to be maintained below a certain threshold. The cyclical admission and the cracks or gaps present in the crude oil reservoir prevent a water quantity, which is too large, from reaching into the conveyor line. In the case of a suitable variation of the conveying rates, the cracks and gaps work like drainages, which divert the water from the surrounding layers. The injection of the fluid into the crude oil reservoir thereby simply takes place via horizontal holes in the supply line, which are distributed across the entire periphery of the line. The fluid is thus pressed out of the supply line so as to be distributed in all spatial directions in a spherically even manner.

However, the high consumption of fluids is a disadvantage of the method described in the state of the art so far. For example, in the event that gas is used in the case of a method for the tertiary crude oil production, it must in most cases be transported to the oil well in an extensive manner. Platforms for the oil production in the ocean form an extreme example herein. In the event that carbon dioxide is to be used for the tertiary crude oil production in the case of such crude oil fields, said carbon dioxide must first be brought to the oil platform by ship or by pipeline. In the case of an alternative use of nitrogen for the tertiary crude oil production on such platforms, the nitrogen would have to be produced on location, that is, a small plant for air separation would have to be installed.

SUMMARY OF THE INVENTION

The instant invention is thus based on the object of embodying a method of the afore-mentioned type in such a manner that the use of fluid is minimized.

The instant object is solved in that the fluid is injected into the crude oil-containing layer of rock or earth in a discontinuous manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be defined below in more detail by means of the exemplary embodiments illustrated in the figures.

FIG. 1 shows an exemplary embodiment of the invention for injecting a fluid from two lines, which are located approximately at the same distance from the conveyor line.

FIG. 2 shows an exemplary embodiment of the invention for injecting a fluid from two lines, which are located at different distances from the conveyor line.

DETAILED DESCRIPTION OF THE INVENTION

According to the instant invention, the fluid is injected into the crude oil-containing layer of rock or earth in a discontinuous manner. That is, according to the invention, the fluid is not injected for the entire length of the method for the tertiary crude oil production, but is injected into the crude oil-containing layer of rock or earth in a discontinuous manner only in certain phases or cycles.

Within the scope of this application, a discontinuous injection refers to the fact that the fluid is injected for a certain predetermined period and that this period is followed by a phase, in which no fluid is injected, said phase in turn being followed by a phase of the fluid injection. A discontinuous injection of a gas thus takes place in several regular or irregular pulses or periods, respectively. Within the scope of this application, the injection or the injecting of a fluid refers to the pressing in or introduction of the fluid into the crude oil-containing layer of rock or earth.

Fluid can be conserved in different ways by means of the discontinuous injecting of the fluid according to the invention.

On the one hand, fluid is conserved because the already injected fluid expands in the rude oil-containing layer of rock or earth in the period in which no fluid is injected. The expanding fluid thus forms a fluid cushion, which drives oil in the direction of the conveyor line, where it can be produced. On the other hand, the flow speed of the fluid in the crude oil-containing layer of rock or earth increases after the injecting of the fluid. The crude oil loosens from the rock or from the earth and is further produced with considerably lower pressure. Surprisingly, it became apparent in comparative tests that in the case of a discontinuous injection of the fluid according to the invention, the crude oil sticks to the crude oil-containing layer of rock or earth to a considerably smaller degree than in the case of a continuous injection according to the method of the state of the art. By means of the phases of the non-injection according to the method of the invention, the fluid can surprisingly also remove oil from the crude oil-containing layer of rock or earth. Said oil adheres to small water films or minerals comprising a large surface in the crude oil-containing layer of rock or earth. This fluid mixture, which includes the oil, which was removed in such a manner, can be moved by means of the next injection.

Preferably, the fluid is injected into the crude oil-containing layer of rock or earth in a positioned manner. In this preferred embodiment of the invention, a considerably higher conservation of necessary fluid can be attained in response to a consistent production effect. By means of the positioned injection of the fluid, that is, by means of the specific injection of the fluid in the direction of the conveyor line, the quantity of the injected fluid is additionally minimized during the injection phase. By means of the positioned injecting, the fluid entry no longer takes place into the complete dihedral angle, but only into a partial area. The quantity of the injected fluid is thus minimized. By combining the discontinuous injection according to the invention with a positioned injection, a minimization of the injected fluid quantity can thus be attained in this embodiment of the invention. The discontinuous injection according to the invention leads to the formation of a fluid cushion, which, in the case of a positioned entry, drives the crude oil in the direction towards the conveyor line, where it can be produced above ground. The fluid injection leads to the formation of a fluid cushion. In the case of the discontinuous injection according to the invention, said fluid cushion is set into motion by subsequent injections. In the case of a positioned injection in this embodiment of the invention, this fluid cushion can be moved in the direction from the line to a second line, wherein the second line serves as a conveyor line.

Preferably, the fluid is injected in the gaseous state. Particularly preferably, the fluid consists of nitrogen, carbon dioxide and/or gaseous hydrocarbons, particularly preferably methane. The advantages of the method according to the invention have an effect in particular in the case of the discontinuous injection of gaseous fluids. For the most part, gaseous fluids such as nitrogen or carbon dioxide are not present in sufficient quantities in the vicinity of the crude oil-containing layers of rock or earth. For the most part, these gaseous fluids would thus have to be transported across longer distances. A considerable reduction of the required fluid quantities, as it occurs according to the method according to the invention, considerably improves the efficiency of a method for producing crude oil from a crude oil-containing layer of rock or earth. The gaseous fluid used in each case is thereby advantageously chosen according to the state and structural conditions of the crude oil-containing layer of rock or earth. Gaseous hydrocarbons mix with the crude oil in the layer of rock or earth, thus reduce the capillary forces, which hold the crude oil in the layer of rock or earth and thus facilitate the transport to the conveyor line. A similar effect occurs with the use of gaseous carbon dioxide. Gaseous carbon dioxide mixes with the crude oil and reduces the viscosity. When using gaseous carbon dioxide, a simpler transport of the crude oil in the crude oil-containing layer of rock or earth is thus attained as well.

The economically more cost-efficient nitrogen, however, virtually does not mix with the crude oil. In the case of a repeated injection of gaseous nitrogen, a gas front forms, into which the light hydrocarbons contained in the crude oil from the crude oil-containing layer of rock or earth diffuse. This increases the viscosity of the remaining residual oil, which is thus more difficult to remove from the layer of rock or earth. This disadvantage can be overcome in that an injection phase is followed by an idle phase, in which the remaining oil particles have time to mix with the stored water. This mixture can then be driven to the conveyor line in response to the next injection phase. It is also advantageous for nitrogen that it does not have an aggressive effect on metals and on the layer of rock or earth and that, as compared to carbon dioxide, it is suitable in particular for less permeable layers of rock or earth due to the small density. Nitrogen is thereby preferably injected at an over-static pressure. Nitrogen enters into the reservoir and expands in the provided direction of injection as long as the gas pressure remains. The residual oil in the pore structure can thereby be desorbed and can be moved through the pore structure together with the gas. In the event that the injection is interrupted, the nitrogen gas can also expand laterally in the phase of the non-injection and can thus permeate into pore spaces, in which oil still adheres to small water films or to minerals comprising a large inner surface or in which oil droplets are present in small pores. The oil-water mixture formed in such a manner can be moved in the direction of the conveyor line by means of the next injection.

Depending on the state of the crude oil-containing layer of rock or earth, a combination of one or several of said gaseous fluids can be advantageous. The combination of gaseous carbon dioxide and gaseous nitrogen is hereby particularly advantageous. The two afore-mentioned advantages of both fluids can also be combined by means of the combination of the two fluids.

In another embodiment of the invention, gaseous fluids such as carbon dioxide and liquid fluids such as water are combined. In this embodiment of the invention, carbon dioxide and water are injected so as to alternate, that is, the injection of carbon dioxide is followed by a phase without fluid injection, which in turn is followed by the injection of water. The injected gas thereby causes an improved flowability of the oil and the subsequently injected water causes the formation of oil banks in the borders of the gas flows, which move more or less with straight boundary lines.

Advantageously, the fluid is injected in pulses. In this embodiment of the invention, the fluid is advantageously injected in regular pulses of predetermined length. A pulse is thereby understood to be the time period from start to stop of the injection of the fluid. Advantageously, several pulses of predetermined length are thereby injected consecutively. The injection of different fluids in response to succeeding pulses has also proven to be advantageous. Advantageously, the different mechanisms and advantageous of the respective fluids can simply be combined with one another by means of the injection of different fluids in succeeding pulses. For instance, gaseous carbon dioxide can be injected in a first pulse and the viscosity of the oil in the crude oil-containing layer of rock or earth can thus be reduced. The crude oil now having a lower viscosity can now be driven in the direction of the conveyor line by means of the injection of gaseous nitrogen in the succeeding pulse.

Advantageously, the time lag between two injection pulses is not shorter than the pulse length and is preferably one to ten times the pulse length. By means of the pulsed injection, it is attained that the fluid cushion is reduced by increasing the pressure during the injection process and is subsequently increased again. This effect becomes smaller with decreasing impulse lengths. Measurements have shown that it is even possible for a negative effect to occur in the case of pulse quantities, which are too short. In these cases, the injected fluid substantially escapes again through the line, through which the fluid has been injected, without having driven the oil in the crude oil-containing layer of rock or earth in the direction of the conveyor line. A sufficient pulse period must thus be observed.

The time lag between two injection pulses, that is, the time during which no fluid is injected, must also be sufficiently long. Advantageously, the time lag between two injection pulses is thus not shorter than the pulse length. Measurements have shown that now and then a negative effect occurs in the case of shorter periods, that is, the fluid is not pressed in the direction towards the conveyor line by means of the pulse. However, longer periods are possible. A time lag between two injection pulses, which is one to ten times the pulse length, is preferred for an economically sensible operation.

The period required by the gas to cover half the distance between the line, through which the fluid is injected, and the conveyor line, is particularly preferred as minimal pulse length. In this embodiment of the invention, it is thus ensured that the crude oil is pushed on in the direction of the conveyor line by means of the injected fluid. In the event that measurements relating to the fluid speed in the respective crude oil-containing layer of rock or earth are not available, a speed in the range of from 0.5 m/min to 5 m/min is assumed. The speed is thereby a function of the porosity of the respective crude oil-containing layer of rock or earth. In the case of crude oil-containing layers of rock or earth comprising a high porosity, a high fluid speed can be assumed.

In an embodiment of the invention, the fluid is injected from more than one line in a positioned manner, wherein pulse length, pulse distance and/or start of the injection in the case of at least one line is/are different from pulse length, pulse distance and/or start of the injection in the case of at least one other line. In the event that more than one line is used for the positioned and pulsed injection of fluid flows in the direction of a conveyor line, it is advantageous to inject both fluid flows in a time-lagged manner. Sensibly, one should make sure that the first injected fluid flow has actually arrived in the reach of the second fluid flow. A shifting of the first fluid flow in the direction of the conveyor line thus becomes possible. In the case of an early or late injection of the second fluid flow, the combined fluid flow is conveyed past the conveyor line; pulse length, pulse distance and/or time of the injections must thereby be chosen in such a manner that all of the fluid is injected in the direction of the conveyor line.

In another embodiment of the invention, in the case of which the fluid is injected from two lines, which have the same distance from the conveyor line, it is advantageous to start the pulses at the same time and with the same pulse length, but with different injection direction.

Advantageously, the quantities of injected fluids from at least two lines are adjusted in such a manner that the injected fluid from a first line is diverted in the direction of the conveyor line by means of the quantity of the injected fluid from at least a second line. The quantity of injected fluid from the second line is thereby adjusted in such a manner that it can divert the injected fluid from the first line in the direction of the conveyor line. Advantageously, the quantity of the fluid injected in the second line is similar to the magnitude of the quantity of the injected fluid from the first line. Preferably, the ratio of the quantities of the injected fluids lies between 10:1 and 1:1. Likewise, the direction of the induced fluids from at least two lines is advantageously adjusted in such a manner that the combined fluid flow from the lines is oriented in the direction of the conveyor line.

The instant invention encompasses a number of advantages as compared to the state of the art. In particular the quantity of the induced fluid for the same conveyor capability can be reduced considerably as compared to the state of the art. Fluid is conserved, because the already induced fluid expands in the crude oil-containing layer of rock or earth during the phase, in which no fluid is induced. The speed of the induced fluid in the crude oil-containing layer of rock or earth furthermore increases in phases, whereby the crude oil is removed from the layer of rock or earth to a considerably improved degree than with a fluid flow, which flows continuously at the same speed.

FIG. 1 shows an exemplary embodiment of the method according to the invention, wherein the fluid is injected into the crude oil-containing layer of rock or earth via the two lines 1 and 2. Both lines 1 and 2 are located at approximately the same distance from the conveyor line 3. The gas flow G1 is injected into the crude oil-containing layer of rock or earth from the line 1 in a pulsed manner. The gas flow G2 is also induced into the crude oil-containing layer of rock or earth from the line 2 in a pulsed manner. Pulse durations of approx. 20 min are used thereby. The time lag between two pulses of an injection line is approx. 1 hour. The injected gas quantities G1 and G2 are thereby in the same magnitude in each case. Due to the overlap of the positioned and pulsed gas flows G1 and G2, a resulting gas flow G3 forms, which moves in the direction of the conveyor line 3. The crude oil is thus driven in the direction of the conveyor line 3 by means of the positioned and pulsed gas flows. In this embodiment of the invention, nitrogen and carbon dioxide are injected so as to alternate, so that the different characteristics of both gases can be used for the crude oil production.

FIG. 2 shows an exemplary embodiment of the invention, wherein the fluid is injected into the crude oil-containing layer of rock or earth via two lines 1 and 2. In this exemplary embodiment of the invention, the two lines 1 and 2 are spaced apart from the conveyor line 3 at different distances. In this exemplary embodiment of the invention, the pulsed injection of the fluid from line 1 starts prior to the pulsed injection of the fluid from line 2. This means that the two pulses from line 1 and line 2 are time-lagged. The time lag between an injection pulse in line 1 and an injection pulse in line 2 thereby corresponds to the time, which the fluid induced from line 1 requires to reach into the injection area of the fluid from line 2. In this exemplary embodiment of the invention, the fluid is injected via the line 1 with a pulse length of three hours. After a delay of approx. one hour, the fluid from line 2 is injected with a pulse length of three hours. Pulses with a pulse length of one hour are subsequently injected from both lines. Shorter pulse lengths are used here, because after the 2^(nd) pulse, the fluid cushion in the rock must only be set into motion or maintained in motion, respectively.

A pulse length of one hour is also possible for the injection from line 1 and a pulse length of 2 hours is possible for the injection from line 2 as a function of the characteristic of the respective crude oil-containing layer of rock or earth. In the event that the crude oil-containing layer of rock or earth in the immediate surroundings of line 1 is highly porous, a fluid cushion can establish there very rapidly. In the event that the crude oil-containing layer of rock or earth in the surroundings of line 2 is less porous, longer pulse lengths are used here, because the establishment of a fluid cushion also takes longer. 

1. A method for injecting a fluid into a crude oil-containing layer of rock or earth by means of a suitable line, wherein the line is introduced into the layer of rock or earth and the fluid is injected for the purpose of an enhanced crude oil production from the crude oil-containing layer of rock or earth, characterized in that the fluid is discontinuously injected into the crude oil-containing layer of rock or earth.
 2. The method according to claim 1, characterized in that the fluid is injected into the crude oil-containing layer of rock or earth in a positioned manner.
 3. The method according to claim 1, characterized in that the fluid is injected in the gaseous state.
 4. The method according to claim 3, characterized in that the fluid is selected from the group consisting of nitrogen, carbon dioxide and gaseous hydrocarbons.
 5. The method according to claim 4 wherein said gaseous hydrocarbon is methane.
 6. The method according to claim 1, characterized in that the fluid is injected in pulses.
 7. The method according to claim 6, characterized in that different fluids are injected in succeeding pulses.
 8. The method according to claim 6, characterized in that the time lag between two injection pulses is not shorter than pulse length,
 9. The method according to claim 8, characterized in that the time lag between two injection pulses is one to ten times the pulse length.
 10. The method according to claim 6, characterized in that the period required by the gas to cover half the distance between the line, through which the fluid is injected, and the conveyor line, is chosen as minimal pulse length.
 11. The method according to claim 6, characterized in that the fluid is injected from more than one line in a positioned manner, wherein pulse length, pulse distance and/or start of the injection in the case of at least one line is/are different from pulse length, pulse distance and/or start of the injection in the case of at least one other line.
 12. The method according to claim 9, characterized in that the quantities of induced fluids from at least two lines are adjusted in such a manner that the induced fluid from a first line is diverted in the direction of the conveyor line by means of the quantity of the injected fluid from at least a second line.
 13. The method according to claim 10, characterized in that the direction of the induced fluids from at least two lines is adjusted in such a manner that the combined fluid flow from the lines is oriented in the direction of the conveyor line. 